This application is based upon, claims the benefit of priority of, and incorporates by reference the contents of prior Japanese Patent Application No. 2001-273058 filed Sep. 10, 2001.
1. Field of the Invention
The present invention relates to an air conditioning system for a vehicle capable of performing a hot gas heating function that uses an interior heat exchanger (evaporator) as a radiator for a gas refrigerant by directly introducing a compressor discharged gas refrigerant (hot gas) into the interior heat exchanger during heating.
2. Description of the Related Art
Conventionally, an air conditioning system for a vehicle circulates hot water (engine cooling water) through a heat exchanger during heating in the wintertime, and heats air conditioning air in the heat exchanger by using the hot water as a heat source. In this case, however, when the temperature of the hot water is low, so is the temperature of the air blown into the passenger compartment, and the air conditioning system may fail in attaining the required heating capacity.
In order to solve this inconvenience, Japanese Patent Laid-Open Publication No. Hei. 5-223357 proposes a refrigerating cycle apparatus capable of performing a heating function by using a hot gas heater cycle. According to this conventional apparatus, when a temperature of the hot water is lower than a predetermined temperature such as during the starting of an engine, the hot gas heater cycle for introducing a compressor discharged gas refrigerant (hot gas) into an evaporator by bypassing a condenser is formed, so that the air conditioning system becomes able to perform a heating function by allowing the gas refrigerant to radiate heat into air conditioning air in the evaporator. In other words, the conventional apparatus uses the evaporator, which is a single interior heat exchanger installed inside the air conditioning case, by switching to serve as a cooler during the cooling mode and as a radiator during the heating mode.
Incidentally, when the outside air temperature is xe2x88x9210xc2x0 C. or below, even when the heating function is performed by the hot gas heater cycle, the air conditioning system may still fail in achieving the required heating ability. In view of the foregoing, the inventors of the present invention conducted a study of a combination of the hot gas heater cycle and another auxiliary heating means, such as an electric heater.
It is therefore an object of the present invention to provide an air conditioning system for a vehicle provided with a plurality of heat enhancing means including at least a hot gas heater cycle, in which operations of the plurality of heat enhancing means are controlled in a satisfactory manner without adversely influencing a temperature the driver senses.
Also, because the hot gas heater cycle uses a single interior heat exchanger installed inside the air conditioning case that alternates to serve as a cooler during the cooling mode and as a radiator during the heating mode, condensed water formed due to a cooling and dehumidification action during the cooling mode evaporates during the heating mode, which causes unwanted fogging on the windshield and side and rear windows (hereinafter, referred to collectively as the windows) of a vehicle. It is therefore another object of the present invention to control the occurrence of fogging on the windows of a vehicle associated with an operation of the hot gas heater cycle.
In order to achieve the above and other objects, a first aspect of the present invention provides an air conditioning system for a vehicle including: a hot gas heater cycle for heating air blown into a passenger compartment by directly introducing a discharged gas refrigerant from a compressor in a refrigerating cycle into an interior heat exchanger; and a plurality of heat enhancing means including the hot gas heater cycle as a heat enhancing means for enhancing a passenger compartment heating ability, wherein, when a heating load is large, the plurality of heat enhancing means are activated, and when the heating load is decreased to or below a predetermined value, one of the plurality of heat enhancing means is deactivated.
According to a first aspect of the invention, a temperature of air blown into the passenger compartment is raised by activating the plurality of heat enhancing means including the hot gas heater cycle when the outside air temperature is extremely low and the heating load is large, which makes it possible to enhance the passenger compartment heating ability in an extremely cold region. Moreover, not all of the plurality of heat enhancing means are activated and deactivated simultaneously, and the number of activated heat enhancing means out of the plurality of heat enhancing means is changed in response to a change in the heating load. This makes it possible to control a change in temperature of the air blown into the passenger compartment when the operations of the heat enhancing means are switched. Consequently, it is possible to reduce a change in temperature the driver may feel when the operations of the plurality of heat enhancing means are switched.
A second aspect of the invention provides an air conditioning system for a vehicle according to the first aspect, wherein the hot gas heater cycle is deactivated when the heating load is decreased to or below the predetermined value. According to the second aspect, the hot gas heater cycle is activated only in extremely cold regions where the heating load is large, and the hot gas heater cycle is deactivated when the heating load is decreased to or below the predetermined value. Consequently, it is possible to control the occurrence of fogging on the windows of a vehicle associated with an operation of the hot gas heater cycle.
To be more specific, in a region where the heating load is small, a temperature of the interior heat exchanger rises higher by the operation of the hot gas heater cycle as the heating load becomes smaller. Hence, when condensed water adheres onto the surface of the interior heat exchanger, the condensed water readily evaporates, which causes unwanted fogging on the windows of a vehicle. However, according to the second aspect of the invention, the hot gas heater cycle is deactivated in the region where the heating load is small and therefore the condensed water readily evaporates. Hence, it is possible to control the occurrence of fogging on the windows of a vehicle by controlling evaporation of the condensed water from the interior heat exchanger.
A third aspect of the invention provides an air conditioning system for a vehicle, including: a hot gas heater cycle for heating air blown into a passenger compartment by directly introducing a discharged gas refrigerant from a compressor in a refrigerating cycle into an interior heat exchanger; and a plurality of heat enhancing means including the hot gas heater cycle as heat enhancing means for enhancing a passenger compartment heating ability. The operations of the plurality of heat enhancing means are controlled in response to a change in a heating load and when the plurality of heat enhancing means are deactivated due to a decrease of the heating load, the hot gas heater cycle is deactivated, after which the heat enhancing means, other than the hot gas heater cycle, are then deactivated.
According to the third aspect, the hot gas heater cycle is deactivated in a region where the heating load is small and therefore condensed water readily evaporates. Consequently, as with the second aspect, it is possible to control the occurrence of fogging on the windows of a vehicle. Also, the operational advantage attained in the first aspect can be provided as well.
A fourth aspect of the invention provides an air conditioning system for a vehicle, including a hot gas heater cycle for heating air blown into a passenger compartment by directly introducing a discharged gas refrigerant from a compressor in a refrigerating cycle into an interior heat exchanger and a plurality of heat enhancing means including the hot gas heater cycle as heat enhancing means for enhancing a passenger compartment heating ability. Operations of the plurality of heat enhancing means are controlled in response to a change in a heating load and when the plurality of heat enhancing means are deactivated due to a decrease of the heating load, the hot gas heater cycle is deactivated first.
According to the fourth aspect, when the heating load is decreased, the hot gas heater cycle is deactivated first, and then the heat enhancing means other than the hot gas heater cycle is deactivated. Consequently, the same operational advantage as in the third aspect can be provided.
A fifth aspect of the invention provides an air conditioning system for a vehicle according to any one of the first through fourth aspects, which is arranged in such a manner that an electric heater is included as the heat enhancing means other than the hot gas heater cycle. This makes it possible to readily enhance the passenger compartment heating ability with the electric heater.
A sixth aspect of the invention provides an air conditioning system for a vehicle according to any one of the first through fifth aspects, which is arranged in such a manner that the heating load can be judged based on at least one of an outside air temperature, an inside air temperature, and a blowing air temperature of the interior heat exchanger.
A seventh aspect of the invention provides an air conditioning system for a vehicle according to any one of the first through sixth aspects, but further including a hot-water heat exchanger for heating the air blown into the passenger compartment using hot water as a heat source. The plurality of heat enhancing means forms auxiliary heating means with respect to the hot-water heat exchanger.
According to the seventh aspect, when the heating load is large, a main heating operation by the hot-water heat exchanger is combined with an auxiliary heating operation by the plurality of heat enhancing means, which makes it possible to quickly begin passenger compartment heating.
An eighth aspect of the invention provides an air conditioning system for a vehicle according to the seventh aspect, wherein a temperature of the hot water circulating through the hot-water heat exchanger is detected, and operations of the plurality of heat enhancing means are controlled depending on the temperature of the hot water. According to the eighth aspect, it is possible to activate the plurality of heat enhancing means only when the main heating ability of the hot-water heat exchanger is insufficient.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.